Chapter 3 Excavating and Lifting Part 2. 3-4 DRAGLINES Operation and Employment Production Estimating Job Management

Chapter 3Excavating and Lifting

Part 2

3-4 DRAGLINES

• Operation and Employment• Production Estimating• Job Management

Operation and Employment• The dragline is a very versatile machine that

has the longest reach for digging and dumping of any member of the crane-shovel family.

• It can dig from above machine level to significant depths in soft to medium-hard material. The components of a dragline are shown in Figure 3-10.

FIGURE 3-10: Components of a dragline.

3-4 DRAGLINES• Bucket teeth and weight produce digging

action as the drag cable pulls the bucket across the ground surface.

• Digging is also controlled by the position at which the drag chain is attached to the bucket (Figure 3-11).

• The higher the point of attachment, the greater the angle at which the bucket enters the soil.

FIGURE 3-11: Dragline bucket.

3-4 DRAGLINES• During hoisting and swinging, material is

retained in the bucket by tension on the dump cable.

• When tension on the drag cable is released, tension is removed from the dump cable, allowing the bucket to dump.

3-4 DRAGLINES• Buckets are available in a wide range of sizes

and weights, solid and perforated. • Also available are archless buckets which

eliminate the front cross-member connecting the bucket sides to provide easier flow of material into and out of the bucket.

3-4 DRAGLINES• While the dragline is a very versatile

excavator, it does not have the positive digging action or lateral control of the shovel.

• Hence the bucket may bounce or move sideways during hard digging.

3-4 DRAGLINES• Also, more spillage must be expected in

loading operations than would occur with a shovel.

• While a skilled dragline operator can overcome many of these limitations, the size of haul units used for dragline loading should be greater than that of those used with a similar-size shovel.

3-4 DRAGLINES• The maximum bucket size to be used on a

dragline depends on machine power, boom length, and material weight.

• Therefore, use the dragline capacity chart provided by the manufacturer instead of the machine's lifting capacity chart to determine maximum allowable bucket size.

Production Estimating• The Association of Equipment Manufacturers

[formerly the Construction Industry Manufacturers Association (CIMA)], through its PCSA Bureau, has made studies of cable-operated dragline operations and has developed production tables that are widely used by the construction industry.

• Tables 3-7 to 3-9 are based on PCSA data. Note, however, that these tables are applicable only to diesel-powered, cable-operated draglines.

3-4 DRAGLINES• To estimate dragline production using the

tables, – determine the ideal output of the dragline for the

machine size and material (Table 3-7), – then adjust this figure by multiplying it by a swing-

depth factor (Table 3-9) and a job efficiency factor, as shown in Equation 3-3.• Expected production = Ideal output × Swing-depth factor

× Efficiency (3-3)

– Notice the conditions applicable to Table 3-7 given in the footnote..

3-4 DRAGLINES • To use Table 3-9 it is first necessary to

determine the optimum depth of cut for the machine and material involved from Table 3-8. Next, divide the actual depth of cut by the optimum depth and express the result as a percentage.

3-4 DRAGLINES• The appropriate swing-depth factor is then

obtained from Table 3-9, interpolating as necessary.

• The method of calculating expected hourly production is illustrated in Example 3-4.

EXAMPLE 3-4

Determine the expected dragline production in loose cubic yards (LCM) per hour based on the following information.

Dragline size = 2 cu yd (1.53 m3)

Swing angle = 120o

Average depth of cut = 7.9 ft (2.4 m)

Material = common earth

Job efficiency = 50 min/h

Soil swell = 25%

EXAMPLE 3-4

Solution

Ideal output =230 BCY/h (176 BCM/h)(Table 3-7)

Optimum depth of cut = 9.9 ft (3.0 m) (Table 3-8)

Actual depth/optimum depth = 7.9/9.9 × 100

= 80%

[= 2.4/3.0 × 100

= 80%]

EXAMPLE 3-4

Swing-depth factor=0.90 (Table 3-9)

Efficiency factor =50/60 = 0.833

Volume change factor = 1 + 0.25 = 1.25

Estimated production = 230 × 0.90 × 0.833

×1.25 = 216 LCY/h

[= 176 × 0.90 × 0.833

×1.25 = 165 LCM/h]

Job Management

• Trial operations may be necessary to select the boom length, boom angle, bucket size and weight, and the attachment position of the drag chain that yield maximum production.

• As in shovel operation, maximum production is obtained with a minimum swing angle.

Job Management

• In general, the lightest bucket capable of satisfactory digging should be used, since this increases the allowable bucket size and reduces cycle time.

• It has been found that the most efficient digging area is located within 15° forward and back of a vertical line through the boom point, as illustrated in Figure 3-12.

Job Management

• Special bucket hitches are available which shorten the drag distance necessary to obtain a full bucket load.

• Deep cuts should be excavated in layers whose thickness is as close to the optimum depth of cut as possible.

FIGURE 3-12: Most efficient digging area for a dragline

3-5 CLAMSHELLS

• Operation and Employment• Production Estimating• Job Management

3-5 CLAMSHELLSOperation and Employment• When the crane-shovel is equipped with a

crane boom and clamshell bucket, it becomes an excavator known as a clamshell.

• The clamshell is capable of excavating to great depths but lacks the positive digging action and precise lateral control of the shovel and backhoe.

3-5 CLAMSHELLS• Clamshells are commonly used for :

– excavating vertical shafts and footings, – unloading bulk materials from rail cars and ships,

and – moving bulk material from stockpiles to bins,

hoppers, or haul units.

3-5 CLAMSHELLS• The components of a cable-operated

clamshell are identified in Figure 3-14. Clamshell attachments are also available for the hydraulic excavator.

• A clamshell bucket is illustrated in Figure 3-14.

• Notice that the bucket halves are forced together by the action of the closing line against the sheaves.

FIGURE 3-13: Components of a Clamshell

FIGURE 3-14: Clamshell bucket

3-5 CLAMSHELLS• When the closing line is released, the

counterweights cause the bucket halves to open as the bucket is held by the holding line.

• Bucket penetration depends on bucket weight assisted by the bucket teeth.

3-5 CLAMSHELLS• Therefore, buckets are available in light,

medium, and heavy weights, with and without teeth. – Heavy buckets are suitable for digging medium

soils. – Medium buckets are used for general-purpose

work, including the excavation of loose soils. – Light buckets are used for handling bulk

materials such as sand and gravel.

3-5 CLAMSHELLS• The orange peel bucket illustrated in Figure

3-15 is principally utilized for underwater excavation and for rock placement.

• Because of its circular shape, it is also well suited to excavating piers and shafts.

• It operates on the same principle as does the clamshell.

FIGURE 3-15: Orange peel bucket.(Courtesy of ESCO Corporation)

3-5 CLAMSHELLS

Production Estimating• No standard production tables are available

for the clamshell. • Thus production estimation should be based

on the use of Equation 2-1. • The procedure is illustrated in Example 3-5.

EXAMPLE 3-5

• Estimate the production in loose cubic yards per hour for a medium-weight clamshell excavating loose earth. Heaped bucket capacity is 1 cu yd (0.75 m3). The soil is common earth with a bucket fill factor of 0.95. Estimated cycle time is 40 s. Job efficiency is estimated at 50 min/h.

EXAMPLE 3-5

Solution

Production = 3600/40 × 1 × 0.95 × 60/50

= 71 LCY/h

B = 3600/40 × 0.75 × 0.95 × 60/50 = 53 LCM/h

Job Management

• The maximum allowable load (bucket weight plus soil weight) on a clamshell should be obtained from the manufacturer's clamshell loading chart for continuous operation.

Job Management

• If a clamshell loading chart is not available, limit the load to 80% of the safe lifting capacity given by the crane capacity chart for rubber- tired equipment or 90% for crawler-mounted equipment.

• Since the machine load includes the weight of the bucket as well as its load, use of the lightest bucket capable of digging the material will enable a larger bucket to be used and will usually increase production.

Job Management

• Tests may be necessary to determine the size of bucket that yields maximum production in a particular situation.

• Cycle time is reduced by organizing the job so that the dumping radius 3-6 Trenching and Trenchless Technology 65 is the same as the digging radius.

Job Management

• Keep the machine level to avoid swinging uphill or downhill.

• Nonlevel swinging is hard on the machine and usually increases cycle time.

3-6 TRENCHING AND TRENCHLESS TECHNOLOGY

• Trenching Machines and Plows• Trenchless Technology• Repair and Rehabilitation of Pipelines


• The use of backhoes and other excavators for digging trenches was discussed earlier in this chapter.

• In addition, there is a growing demand for methods of installing utility systems below the ground with minimum open excavation.


• Some methods available for achieving this objective include specialized trenching machines and plows as well as trenchless technology (also called trenchless excavation).

• Safety considerations in trenching operations are discussed in Section 10-6.


Trenching Machines and Plows• Some of the types of trenching machines

available include chain trenchers, ladder trenchers, and bucket wheel trenchers.

• Figure 3-14 shows a large chain trencher capable of digging 14 to 36 in. (356-914 mm) wide vertical sided trenches to a depth of 10 ft (3.1 m).

• Ladder trenchers are similar to chain trenchers but are larger.

FIGURE 3-16: Chain trencher.(Courtesy of Vermeer Manufacturing Co.)

FIGURE 3-16: Chain trencher.(©Vermeer Manufacturing Company, All Rights Reserved.)


• They are capable of digging trenches up to 10 ft (3.1 m) wide and 25 ft (7.6 m) deep.

• Bucket wheel trenchers use a revolving bucket wheel to cut a trench up to 5 ft (1.5 m) wide and 9 ft (2.7 m) deep.


• Plows can be used to cut a narrow trench and simultaneously insert a small diameter cable or pipeline in most soils.

• Vibratory plows such as those shown in Figure 3-17 deliver a more powerful cutting action than static plows and can be used to insert utility lines in hard soil or soft rock.

FIGURE 3-17: Hydrostatic vibratory plow.(Courtesy of Vermeer Manufacturing Company, All Rights Reserved)

Trenchless Technology

• While a number of different techniques are used in trenchless technology, the principal categories include pipe jacking, horizontal earth boring, and microtunneling.


• The process of pipe jacking (Figure 3-18) involves forcing pipe horizontally through the soil.

• Working from a vertical shaft, a section of pipe is carefully aligned and advanced through the soil by hydraulic jacks braced against the shaft sides.

• As the pipe advances, spoil is removed through the inside of the pipe.

FIGURE 3-18: Installing a utility line by pipe jacking


• After the pipe section has advanced far enough, the hydraulic rams are retracted and another section of pipe is placed into position for installation.

• The process often requires workers to enter the pipe during the pipe jacking operation.


• In horizontal earth boring a horizontal hole is created mechanically or hydraulically with the pipe to be installed serving as the casing for the hole.

• Some of the many installation methods used include auger boring, rod pushing (thrust boring), rotational compaction boring, impact piercing, horizontal directional drilling, and fluid boring.


• A track-mounted thrust boring machine with percussive hammer action is shown in Figure 3-19.

• Many of these techniques utilize lasers and television cameras for hole alignment and boring control.

• A number of types of detectors are available to locate the drill head and ensure that the desired alignment and depth are being maintained.

FIGURE 3-19: Grundodrill & Thrust boring machine with percussive action.

(Courtesy of TT Technologies, Inc.)


• The use of a pneumatic piercing tool to create a borehole for a utility line is illustrated in Figure 3-20.

FIGURE 3-20: Installing a utility line by horizontal earth boring.


• After the bore has been completed, several methods are available to place pipe into the borehole. – In one method, pipe is pulled through the bore

using the tool's air hose or a steel cable pulled by the air hose.

– Another method uses the piercing tool to push the pipe through the borehole.

– A third method uses a pipe pulling adapter attached to the piercing tool to advance the pipe at the same time as the piercing tool advances the bore.


• Microtunneling or utility tunneling is similar to the conventional tunneling described in Section 8-1 except for the tunnel size and use.

• Since the tunnels are used for utility systems rather than for vehicle passage, they are normally smaller than road or rail tunnels.


• They differ from other trenchless methods in their use of a conventional tunnel liner instead of using the pipe itself as a liner.

• Small moles (see Section 8-1) are frequently used in creating such tunnels.

Repair and Rehabilitation of Pipelines

• The repair and rehabilitation of existing pipelines without excavation is another form of trenchless technology.


• While a number of methods exist, most involve the relining of the existing pipeline or the bursting of the existing pipe while inserting a new pipe.

• The relining of a pipeline is accomplished by pulling a new plastic pipe into the existing pipe or by inserting a liner into the existing pipe.


• When a new pipe is used to reline the pipe, the resulting pipe must be slightly smaller than the original pipe.

• Another relining technique involves pulling a folded liner into the existing pipe, expanding the liner, treating the liner with an epoxy, and curing it in place.


• Pipe bursting (Figure 3-21) uses a high-powered hydraulic or pneumatic piercing tool equipped with a special bursting head to shatter the existing pipe and enlarge the opening.

• A new, often larger, pipe is then pulled into the opening by the piercing head.

FIGURE 3-21: Schematic of pneumatic pipe bursting method.

(Courtesy of Earth Tool Company LLC)

FIGURE 3-21: Schematic of pipe bursting.(Courtesy of Vermeer Manufacturing Co.)

Documents

Chapter 3 Excavating and Lifting Part 2. 3-4 DRAGLINES Operation and Employment Production Estimating Job Management